V-] 



THE SKIN DISCHARGE 



83 



direct response, is said by Bach and Oehler not to abolish the 

 indirect excitability, which presumably depends on deeper parts. 

 We therefore conclude that the main factor of the response is 

 the general epithelial investment its Malpighian layer in 

 particular. Indirect excitation of the skin through nervous 

 channels presumably arouses the cutaneous glands alone ; the 

 general epithelium is, as far as we know, as much outside the 

 control of nerve fibres as are blood-corpuscles. 



We cannot, therefore, in comparing the effects of direct and 

 of indirect excitation, regard the comparison as a simple one, 

 like that of direct and indirect excitation of muscle. 



Thus, in frog's skin, the effect of indirect excitation is often 

 negative (ingoing) when that of direct excitation is positive 

 (outgoing). In cat's skin the effect of indirect excitation is 

 always ingoing, that of direct excitation is at first ingoing, at 

 last outgoing. 



It would be interesting to see what effect, if any, the two 

 forms of excitation exercise upon each other. I have not found 

 time to do this, although obviously it would be an easy matter 

 to take a regular series of indirect effects, interpolating in the 

 series one or more direct excitations of some convenient duration 

 and strength ; or a regular series of direct effects, interpolating 

 in the series one or more indirect excitations. Of course, it 

 would be necessary to photograph the effects ; I wonder what 

 they would be ? * 



* I have since tested this point, as regards the effect of direct upon 

 indirect excitation, in the case of frog's skin, also in the case of the cat 

 (vide infra, Lecture VI.), with the following results : 



VoU 

 OO6-1 



003- 

 003- 

 OOI - 

 OOO- 



Before 



After. 



FlG. 37. Indirect responses of frog's skin to tetanisation of the sciatic nerve 

 before and after direct excitation of the skin itself by a single strong induction 



shock D. 



[For continuation of Note, see next page. 



